Remove, and then reinstall the imaging unit or imaging kit.
Warning—Potential Damage: Do not expose the imaging unit or imaging kit to direct light for more than 10 minutes. Extended exposure to light may cause print quality problems.
Warning—Potential Damage: To avoid damage, do not touch the underside of the imaging unit or imaging kit.
Print the document.
Does gray background still appear on prints?
Contact customer support.
The problem is solved.